Labelled diagram of the Special:Upload form, showing various system messages.

A system message is a snippet of plain text, wiki text, CSS, or Javascript that can be used to customize the behavior of MediaWiki and its appearance for each language and locale. MediaWiki uses messages for any user-facing part of the interface, allowing for internationalization and localization of the MediaWiki UI, for both core and extensions.

Contents

Messages in the source code

Overriding messages on-wiki

In addition to this, messages can be overridden from their default values by editing them on-wiki. Each message has a wiki page in the MediaWiki namespace with its message key as the name of the page. For example, the "aboutsite" message is stored at MediaWiki:aboutsite. By default this namespace is restricted from editing unless the user has the "editinterface" permission. A list of all message pages can be found on Special:AllMessages. Editing interface messages is typically straightforward, just like editing a normal wiki page, but it is restricted to users with the editinterface permission, which is assigned to interface administrators by default.

The Special:AllMessages table contains two columns: the linked interface name, and the text. The text is horizontally split to show the default text above, and the customized text below. When a custom message does not exist, only the default will be shown. To customize a message, click the upper link in the left column (the name of the message). This link is red if the default text is in use, because the edit page is empty.

The lower links in the left column cells lead to the discussion pages for that message.

In MediaWiki 1.18 and above, you can find a message key by browsing a wiki in the special pseudo-language code qqx, which can be done by appending ?uselang=qqx to the URL, or &uselang=qqx if the URL already contains a ? character (example). All the messages will then be replaced by their message keys, so you can identify which message is responsible. Messages that are always in the content language will not be shown using qqx.

Some parts of the interface add nstab- to the string that is shown when you use the qqx trick. For example the label for the tab that links to the discussion page in the main namespace is shown as nstab-talk, but the string is actually located at MediaWiki:Talk.

In case the page uses tabs like e.g. special page "Preferences" you will have to add the tab after the uselang parameter, e.g. Special:Preferences?uselang=qqx#mw-prefsection-rendering.